1. Field of the Invention
This invention relates generally to data recording systems, such as magnetic recording hard disk drives, and more particularly to pre-recorded servo patterns and servo positioning systems to locate and maintain the read/write heads on the data tracks.
2. Description of the Related Art
Magnetic recording hard disk drives use a servo-mechanical positioning system to hold the read/write head on the desired data track and to seek from track to track as required to perform read and write operations. Special “servo” information is written in fields in circumferentially-spaced servo sectors in each of the concentric data tracks on each disk surface. The servo pattern is constructed across multiple tracks so that the readback signal from the head, as it passes over the pattern, can be decoded to yield the position error signal (PES) that represents the radial position of the head. The servo pattern is written onto the disk during manufacturing in a process known as servowriting. In conventional servowriting the servo pattern is written in multiple passes using the regular write head in conjunction with a specialized servowriter. The servo pattern may also be written using a magnetically printed preliminary pattern followed by a detailed final pattern, by a media-level servowriter (e.g., a stack of 10 disks servowritten with servowriting heads), or by self-servowriting by the disk drive without a specialized servowriter.
One common servo pattern is a quad-burst pattern of four fields of PES bursts. The standard PES decoder for the quad-burst pattern is relatively complex hardware or software that uses sinusoidal processing techniques, such as a single-point discrete Fourier Transform (DFT).
It is desirable to reduce the amount of disk surface area used by the servo pattern. The standard and most straightforward approach to achieve this reduction is to increase the frequency (or density) of the information in the servo pattern. However, this approach is limited by the tradeoff between servowriter yield, costs to upgrade the servowriter, and increased complexity of the PES decoder.
What is needed is a servo pattern that is easy to servowrite, reduces the amount of disk surface area required, and does not require complex signal processing hardware or software to decode the PES.